1. Field of the Invention
The present invention relates to a method for sheathing a substrate with a fluorine resin tube, and a fixing member which is fabricated by the method and used in electrophotographic image-forming apparatuses such as copying machines and laser beam printers.
2. Description of the Related Art
Typical known methods for sheathing a substrate with a fluorine resin tube on a hollow or solid cylindrical substrate include:
1) Applying a bonding agent onto the surface of a rubber roller, which has been previously fabricated, sheathing the surface with a heat-shrinkable fluorine resin tube, and bonding it to the substrate by heat shrinkage; and PA1 2) Placing a fluorine resin tube, in which a bonding agent is applied on the preliminarily treated inner surface, into a cylindrical mold, and then injecting a liquid rubber between the fluorine resin tube and a core bar.
In these processes, bonding of the fluorine resin tube is generally performed at a temperature which is considerably lower than the melting point of the fluorine resin in order to ensure processability and to prevent deterioration of the rubber of the base layer.
Typical methods for fixing rollers, which are used as fixing members in electrophotographic image-forming apparatuses, include: sheathing a metallic substrate with a heat-shrinkable fluorine resin tube as a toner-releasing layer followed by bonding by means of a hot melt process; forming a heat-resistant rubber layer on a metallic core bar and bonding a heat-shrinkable fluorine resin tube as a toner-releasing agent thereon by the above-mentioned process; and sheathing a substrate composed of metal and a heat-resistant resin formed thereon with a heat-shrinkable fluorine resin tube as a toner-releasing layer, followed by bonding by means of a hot melt process. A typical method for making fixing belts includes forming a heat-resistant rubber layer on a film composed of a metal or heat-resistant resin film and bonding a heat-shrinkable fluorine resin tube as a toner-releasing agent thereon by the above-mentioned process. Also, a typical method for fabricating a pressure roller includes forming a heat-resistant rubber layer onto a metallic core bar and then bonding a fluorine resin tube as a toner-releasing agent thereon by the above-mentioned process.
The above-mentioned methods for sheathing the substrates with the fluorine resin tubes, however, have the following problems. Each fluorine resin tube is bonded to the rubber layer of the substrate with an adhesive agent since the bonding process is performed at a temperature which is considerably lower than the melting temperature of the fluorine resin in order to prevent the deterioration of the rubber layer of the substrate. When flaws form on the tube, peeling by stress will easily occur between the tube and the rubber, or dead folds or wrinkles will be observed on the tube. Since the fixing roller is always heated, the strength of the fixing roller gradually decreases as a result of deterioration from long-term use, and thus wrinkles form which will cause to be less smooth or will cause a rupture. Although the bonding strength is improved by the treatment of the inner surface of the fluorine resin tube, such as chemical treatment, such a treatment requires particular chemicals and equipment, resulting in high production costs. Further, the treated surface will be rapidly changed by its environment.
Accordingly, it is difficult to easily and stably sheath a fluorine resin tube by bonding such that the resulting roller has sufficient heat resistance and strength. Further, the fluorine resin sheath does not have a smooth surface for practical use.